Method of continuously casting aluminum for simultaneous production of plural ingots

ABSTRACT

In the continuous casting of aluminium a series of moulds are supplied with molten metal through individual dip tubes from a common trough system. To approximately synchronise entry of metal to the moulds, the mouth of each dip tube is initially closed by means of a buoyant plug to prevent entry of metal to the dip tube, until a predetermined depth of metal has been established in the trough system.

United States Patent Snider Aug. 20, 1974 [54] METHOD OF CONTINUOUSLYCASTING 3,224,460 12/1965 Cann 137 399 ALUMINUM FDR SIMULTANEOUS3,332,474 7/1967 Sickbert 164/64 X PRODUCTION OF PLURAL INGOTS Inventor:

[75] James Roy Snider, Kingston,

Ontario, Canada [73] Assignee: Alcan Research and Development Limited,Montreal, Quebec, Canada Filed: Dec. 15, 1972 App]. No.: 315,500

References Cited UNITED STATES PATENTS 10/1940 Junghans 164/281 FOREIGNPATENTS OR APPLICATIONS 72,085 5/1947 Norway ..164/281 448,396 3/1968Switzerland 164/281 Primary Examiner-R. Spencer Annear Attorney, Agent,or Firm-Dunham, Cooper, Clark, Griffin & Moran [57] ABSTRACT In thecontinuous casting of aluminium a series of moulds are supplied withmolten metal through individual dip tubes from a common trough system.To approximately synchronise entry of metal to the moulds, the mouth ofeach dip tube is initially closed by means of a buoyant plug to prevententry of metal to the dip tube, until a predetermined depth of metal hasbeen established in the trough system.

5 Claims, 2 Drawing Figures PATENIEDAUBZOIHH I The present inventionrelates to the continuous casting of aluminum (including aluminiumalloys). In the continuous casting of aluminium it is conventional tocast a number of ingots in a single operation. It is common practice tocast as many as 48 ingots simultaneously. The metal is distributed froma holding furnace to the individual moulds via a trough system, fromwhich it enters the moulds through dip tubes. The lower ends of themoulds are initially closed by means of stools, which are mounted on acommon table. The table is supported by a hydraulic ram to permit it tobe lowered at a controlled rate. Each dip tube is provided with a float,which closes the bottom end of the dip tube when the level of metal inthe mould rises above a predetermined value.

At the beginning of the casting operation it is inevitable that themetal poured into the trough system will reach and enter the mouth ofsome of the dip tubes in advance of reaching the remainder of the diptubes and this presents certain difficulties in controlling the pouringof the ingots. Since the lowering of the table cannot be commenced untila pool of metal of a predetermined depth has been established in each ofthe moulds, solidification will have proceeded to differing extents inthe moulds if the metal commences to enter some dip tubes before others.i

It is an object of the present invention to overcome this difficulty bypreventing the entry of metal into a dip tube until there is apredetermined depth of metal in the trough at the dip tube locality.Although this does not result in exact synchronisation of entry of metalinto all the dip tubes it is found in fact to overcome previouslyexperienced difficulties.

In order to achieve this result according to the present invention eachof the dip tubes is provided with a buoyant plug of a material which issubstantially unaffected by molten aluminum. Each of these plugs has astem, which fits loosely within the mouth of the dip tube and anenlarged head. It will be appreciated that the stem of the plug must beof sufficient size to prevent displacement of the plug by the stream ofmetal poured into the trough system. The enlarged head of the plug mustprovide sufficient buoyancy in molten aluminium to lift the total weightof the plug, formed by the head and stem since initially the stem willbe out of contact with the aluminium. Preferably the stem, althoughfitting loosely into the mouth of the dip tube, is a sufficiently closefit to prevent any substantial flow of metal into the dip tube until thelower end of the stem has been lifted out of the tube by reason of therise of the metal level in the trough'system. The stem and head may beso dimensioned in respect to each other that, after being lifted out ofthe mouth of the dip tube, the plug turns on its side, thus precludingthe possibility of reentering the mouth of a dip tube and closing it offbefore the trough system has emptied itself. It will be seen that theplug must be formed of a material which has a substantially lowerspecific gravity than molten aluminum since the head must provide thebuoyancy to lift both itself and the stem at the beginning of theoperation. In general it may be said that the specific gravity of theplug should not exceed three quarters of the specific gravity of moltenaluminium and more preferably does not exceed one quarter of suchspecific gravity.

In the accompanying drawings:

FIG. 1 illustrates a typical trough system to which the presentinvention may be applied, and

FIG. 2 is a detail of a plug in the mouth of a dip tube.

In the system of FIG. 1 metal is distributed from a holding furnace to aplurality of conventional continuous casting moulds 1 through a troughsystem 2, the entry to. each mould from the trough system being throughdip tubes 3. In FIG. 1 for convenience a single casting mould 1 isindicated diagrammatically. A float 4 is provided in each mould l tocontrol the flow of metal through the dip tube 3 during the castingoperation. The bottom end of each dip tube is initially open, the float4 being supported by a pair of support wires 5, which rest on the top ofthe mould. In FIG. 1 the top of each dip tube 3 is indicated at 6. Itwill however be understood that the number of dip tubes will commonly befar in excess of the number indicated in FIG. 1. Each dip tube isprovided with a plug 16. In operation the metal from a holding furnaceenters the trough system through a launder 12 so that normally the metalreaches and commences to enter some dip tubes in advance of others.

In FIG. 2 the normal operating level of metal in the trough during thepouring of the ingots is indicated by the chain line 15. It is desiredto retard the entry of metal into the dip tubes 3 until the metal levelin the trough 2 is approaching this level.

The plug 16 illustrated in FIG. 2 is made of marinite, a refractoryhaving a specific gravity of about 0.6, as compared with the specificgravity of 2.7 of molten aluminium. The plug 16 has a head 17 which maybe frusto-conical, as illustrated, or which may be cylindrical or othershape, as desired. The head 17 has a flat undersurface 18 to seal offthe mouth of the dip tube 3 although it is unnecessary for such a sealto exist in order for the apparatus to function effectively. The stem 19of the plug has a diameter of about 0.040 inches (about 1 mm.) less thanthe internal diameter of the dip tube 14, so that it can rise freely inthe dip tube, and so that it can move freely therein without permittingentry of molten metal until the stem is fully withdrawn from the diptube. However a greater clearance than this may be employed sincesurface effects will retard the entry of the molten metal into thenarrow gap between the stem 19 and the wall of the dip tube. The lengthof the stem 19 controls the level to which the metal must rise in thetrough before the dip tube is opened to the entry of metal. In FIG. 2the stem 19 is not fully withdrawn until the metal level reaches theline 25. Thus the mouth of each dip tube is maintained in a closedcondition until a substantial depth of metal has been established in thetrough 2 in its locality. This expedient is found to result in adequate,although not exact, synchronisation of the entry of metal to thedifferent dip tubes of a multimould casting apparatus. It will beunderstood that the dimensions of the head 17 must be such as to providesufficient buoyancy for the whole plug. Thus it may be necessary toincrease the dimensions of the head if the length of the stem isincreased. As already stated, there is no difficulty in designing theplugs so that they turn to a substantially horizontal position.

An advantage of the use of the dip tube plugs of the present inventionis that dross on the surface of the to the individual mouldscharacterised by the steps of introducing molten aluminum into saidtrough with each dip tube being fitted with a buoyant plug member forpreventing flow of metal through the dip tube until the local metallevel has attained a predetermined value, each of said plugs beingformed of a material substantially unaffected by molten aluminium andeach of said plugs having a substantially lower specific gravity thanmolten aluminum and comprising a head of greater width than the mouth ofthe dip tube and a stern having a diameter slightly less than theinternal diameter of the dip tube to permit movement freely thereinwithout permitting access of molten aluminium, the size of the head ofthe plug being sufiicient to provide buoyancy for the whole plug andcontinuing to supply molten metal to the trough with the plugs floatingfree of the dip tubes.

2. A method according to claim 1 in which the plugs have a specificgravity less than one quarter of the specific gravity of moltenaluminium.

3. A method according to claim 1 wherein the specific gravity of eachsaid plug is not greater than three quarters of the specific gravity ofmolten aluminum.

4. A method according to claim 1 wherein each said plug is shaped toturn through a substantial angle upon floating free of the dip tubemouth for preventing reentry of the plug into the dip tube mouth.

5. A method according to claim 1 wherein the head of each said plug hasa flat under surface for sealably closing the mouth of a dip tube whenthe plug is fitted in the dip tube mouth.

1. A method of continuously casting aluminium to produce a plurality ofingots simultaneously by supplying metal to a plurality of castingmoulds by means of a trough system fitted with individual dip tubesleading to the individual moulds characterised by the steps ofintroducing molten aluminum into said trough with each dip tube beingfitted with a buoyant plug member for preventing flow of metal throughthe dip tube until the local metal level has attained a predeterminedvalue, each of said plugs being formed of a material substantiallyunaffected by molten aluminium and each of said plugs having asubstantially lower specific gravity than molten aluminum and comprisinga head of greater width than the mouth of the dip tube and a stem havinga diameter slightly less than the internal diameter of the dip tube topermit movement freely therein without permitting access of moltenaluminium, the size of the head of the plug being sufficient to providebuoyancy for the whole plug and continuing to supply molten metal to thetrough with the plugs floating free of the dip tubes.
 2. A methodaccording to claim 1 in which the plugs have a specific gravity lessthan one quarter of the specific gravity of molten aluminium.
 3. Amethod according to claim 1 wherein the specific gravity of each saidplug is not greater than three quarters of the specific gravity ofmolten aluminum.
 4. A method according to claim 1 wherein each said plugis shaped to turn through a substantial angle upon floating free of thedip tube mouth for preventing re-entry of the plug into the dip tubemouth.
 5. A method according to claim 1 wherein the head of each saidplug has a flat under surface for sealably closing the mouth of a diptube when the plug is fitted in the dip tube mouth.